Replace all uses of Perl <> with <<>>.

I've only just found out that it has the effect of treating the argv
words not as plain filenames, but as arguments to Perl default 'open',
i.e. if they end in | then the text before that is treated as a
command. That's not what was intended in any of these contexts!

Fortunately, in this project it only comes up in non-critical
'contrib' scripts.